#include <stdio.h>
// 双指针法
void reverse(char s[]) {
        // Please fill this blank
        int i, j;
        for (i = 0, j = strlen(s)-1; i < j; i++, j--) {
                s[i] ^= s[j];
                s[j] ^= s[i];
                s[i] ^= s[j];
        }
}
